BOPs are commonly used for well control in oil and gas wells and other subterranean exploration and production activities, especially during drilling operations, completion operations, and production of hydrocarbons (or other matter) encountered under pressure from a well. The use of BOPs is required by law in most regions where oil and gas drilling operations are performed
BOPs have been used in the oil and gas industry for nearly a century, as illustrated in U.S. Pat. No. 1,569,247, which is incorporated by reference herein in its entirety. Conventional BOPs utilize radially opposing hydraulic ram blocks. As hydraulic fluid is forced into a piston configured within the rams inside each ram module, the rams converge (e.g., move in an inward direction), typically to contact one another to seal a wellbore. While rams can be used to cut and/or displace a tubular, or seal around a tubular, various types of BOPs can be used to seal a well independent of whether the wellbore contains a tubular. Controlling unwanted or unexpected pressure in a wellbore is critical to maintaining a safe work environment and safe equipment, and preserves both the environment and the reservoir.
Different types of BOPs have evolved over the years to address different problems in various drilling scenarios. Standard practice in the offshore oil and gas industry is the use of tall “stacks” of multiple BOPs, which may vary in type, configuration, as well as redundancy of features.
Standard practice in the oil and gas industry involves use of ram-type blowout preventers. Ram-type blowout preventers are generally regarded as reliable in situations in which the highest, most dangerous pressures may be encountered. Since the development of the first BOPs in the 1920s, the design/configuration of ram-type BOPs has changed only slightly, at least in terms of mechanical function, and these changes are generally limited to the addition of hydraulic force and modern controls. Radially opposing ram blocks, that is, ram blocks positioned on opposite sides of the wellbore and contained in a BOP housing, are generally hydraulically actuated to “close”, and make contact in the center of the wellbore, providing a seal against wellbore pressure. In this closing operation, a seal may be formed around any tubular in the wellbore, through contact between rams if using blind ram blocks (e.g. no tubulars), or through contact between rams when shear rams are used, e.g., to shear and seal tubular(s). The rams generally include ram block sealing surfaces formed from extendable, expandable, extrudable rubber, or rubber “packers” on the ends thereof, that are formed with the required shape and flexibility to form a seal around a tubular, or against an opposing ram in the case of shearing or in the absence of a tubular.
The BOP housing that contains the ram cavity and ram blocks has an open center for placement over the wellbore and allowing space for tubulars, such as a drill string, that may pass through the BOP housing and into or above the wellbore. Recently, in order to generate sufficient pressure during actuation to shear tubulars of significant strength, the movement of pistons in the rams requires a great deal of external room—significant external space sufficient for placement of large hydraulic cylinders and an accordingly large amount of hydraulic fluid. This required space is seen in the form of the lateral extension of roughly linear hydraulic cylinders away from, and transverse or perpendicular to, the main BOP housing, and opposite an opposing ram block. The introduction of hydraulic fluid under pressure into the cylinder actuates the ram(s) toward a closed position. Thus, large cylinders and external housings (extending in opposite directions from the ram block, laterally outward from the BOP housing) are critical to the function of conventional BOPs. These cylinders with their external housings require great amounts of space in both lateral directions and add great mass to the entire BOP in order to increase force necessary to execute a closing operation. As such, conventional BOPs possess a large and unwieldy footprint, requiring extensive planning as well as powerful equipment for placement over the wellbore.
U.S. Pat. No. 7,779,918, which is incorporated by reference herein in its entirety, describes a compact wellbore control device that utilizes hydraulic pistons to actuate linkages that in turn force rams together in a “close” operation. This wellbore control device appears to provide a relatively compact, although mechanically complex, means of severing a small diameter tubular, such as the referenced workstring, within a riser pipe, but is primarily suitable only for operations performed on a relatively small diameter tubular.
U.S. Pat. No. 8,353,338, which is incorporated by reference herein in its entirety, describes an alternate means of hydraulically moving a shear assembly outward with the trailing edge of a shear assembly, rather than the leading edge, moving slightly across the wellbore and executing the shear of a tubular. As noted, traditional ram BOPs utilize the leading edge of a shear assembly that is making an inward, or toward and then slightly across the wellbore movement, in a sealing and shearing operation.
It should be well noted that tubular shearing (and resultant sealing) operations require more force than other BOP closing operations. Typically, the increased energy required for shearing operations is generated by adding booster cylinders to the end of existing ram hydraulic cylinders. The added booster cylinders add mass and further increase the already-large BOP footprint.
A flanged, bolt-on “bonnet,” or a hinged “door,” with a contiguous (from the flange or door) extended hydraulic cylinder housing is the typical means by which a conventional BOP cylinder is attached the BOP housing. As described previously, this flanged or hinged housing extends perpendicularly or transversely outward from the main BOP housing. Such bonnets are typically bolted to the main BOP body with a number of large, heavy bolts, while hinged doors are joined to the main BOP body by large hinges. Removal of the bolts and/or hinges is a very time-intensive and laborious endeavor. In recent years, “boltless” doors have been developed, which utilize a different locking mechanism, though large hinges on the doors still consume significant space, which is compounded by the large swing-arc space required to open the door. Accommodations for large hinge doors may interfere with placement of other equipment and/or service efforts under certain circumstances.
Ram BOPs traditionally utilize “open” and “close” ports in the BOP body to channel hydraulic fluid to the rams and actuate them toward the open or close position, respectively. As fluid enters one end of a ram cylinder on one side of the piston-ram-shaft assembly, it will displace fluid contained in the cylinder on the other side of the piston. BOPs are designed with appropriate ports, passageways and accumulators to accommodate the fluid movement that actuates a BOP between open and close positions. A closing operation closes the rams when required, and the “open” operation retracts the rams to an open position when deemed appropriate and safe.
Conventional BOPs are relatively reliable, if cumbersome, having a significant number of moving parts and wear parts. The power of a conventional BOP to deliver sealing or shearing force remains closely correlated to the BOP's size, with an increase in deliverable force resulting in a significant increase in the footprint of the BOP. Due to the fact that modern wells are drilled to significant depths and encounter very significant pressures, both on land and in offshore subsea installations, BOPs and BOP stacks are becoming extremely heavy and occupy enormous footprints. Yet even with the size and power of conventional BOPs, serious pressure-related oilfield accidents and mishaps continue to plague the industry.